Why using this small spacer on the top of the stem (Team Emirates)?

Discuss light weight issues concerning road bikes & parts.
1415chris
Posts: 1093
Joined: Sat Apr 18, 2009 8:59 am
Location: Surrey UK

by 1415chris

If you loosing preload it must be something wrong with the stem assembly or steerer tube in the first place.
Look at Canyon bikes for instance, no top cup, just a plug.

User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

I get what you are saying, but if you have a stem that's rotating on your steerer, then having proper preload is probably the least of your concerns. And if you didn't have a top cap, and you lost your preload (the only way that could happen is if the stem bolts loosened off), then you just push down on the stem and get as good a preload as you can and lock it down with the stem bolts, as it should have been in the first place. You could still get home just fine. But there's no way I'd ride with loose stem bolts and just the top cap holding my stem on, anchored by a fairly easily sliding expansion plug. And keep in mind that that are systems (like Canyon) that don't need the top cap at all. These bolts are a very good application to use Loctite on. Most stem bolts come with loctite already applied these days on high end stems, but if not, or if you've removed them and the loctite is gone, it's a good idea to reapply before reiinstalling.

But here's why I do like support inside the steertube, aside from just providing an anchor for the top cap to provide preload... If there is nothing inside then over time, the jarring and movement could actually allow the stem to "walk" up the steertube a bit. It's not going to fly off and you'll notice a loose headset well before anything like that happens (note how Sagan was tightening down his stem on the fly during this years Paris Roubaix), but it's just good sound design to have something supportive where the clamping forces are occuring.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

by Weenie


User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

thePrince wrote:
Thu May 17, 2018 5:42 pm
And one more thing re the top cap. The steerer is made to carry the compression load vertically. If you remove the top cap and apply all of the load through the stem, you would eventually delimante your steerer (vibratations and movements from the handlebar naturally causing that shear load if no vertical compression).
Ahh... no, the preload is very nominal, like 12inch/lbs in a lot of cases... just enough to take all the slack out of the system, in the same way as you adjust the bearings in cup and cone hubs. Not overly tight or the bearings would bind. Once the slack is out, the stem bolts are what locks everything down. Toss the top cap if you like, unless it's an integral part of the supportive system, as is the case with TIME bicycles for example, where while the preload is all set below the stem and in the headset, the integrated top cap and supportive alloy sleeve is still an integral part of the suupportive structure.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

thePrince
Posts: 115
Joined: Sun Jun 16, 2013 1:09 am

by thePrince

Yeah that's my point, it's not the case for every setup that the top cap is 100% essential, but for generic guidance as people are reading it should be considered that way to be safe. And regarding the vertical compression I was mentioning, the "walk up" is exactly what would lead to more shear force. The stem walks up, creating slack in the system, which in turn allows the fork to rock back and forth a bit. Not ideal. And if you ran no spacer on the top like some do, and had no top cap, and the stem walks up, now you are potentially crushing the top lip of the fork if you have a recessed plug.

I'm just saying that a lot of shit can go wrong and there is a reason that the top cap is not an installation tool but is integral part of the system. Calnago - remember a lot of people are not like you or myself who are anal about their setup and would notice a slight creak and fix it before the next ride. Some are set and forget and would ride through the creaking if their headset is loose or might just assume its their BB30 creaking since these noises echo around carbon frames/wheels/bars/seat posts/ cranksets. So why suggest not using the top cap for these kinds of riders when something could definitely go wrong - espcially a home mechanic without a ton of experience who just reads one post on the internet, sees it's ok to toss the top cap, doesn't adjust the preload correctly, and goes out for a ride.

User avatar
TonyM
Posts: 2482
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM


Image

I just checked my stem and discovered that the LBS cut the steerer a few millimetres below the top of the stem - although it has a 5mm spacers on top of it.

Is this supposed to be like this?

If not correctly done, what is the optimal height of the steerer when having a 5mm spacer on top?



User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

If I was using a 5mm spacer on top I’d leave a ~1mm or so lip protruding above the stem. That provides and necessary “placeholder” for the added spacer and prevents it from sliding around on top. The main reason I use a small spacer on top is so I can get full contact between the stem and steertube. But I need a gap between the compression plug and the underside of top cap to be able to apply any preload. The 5mm spacer provides that gap.
As long as the steertube is not cut below where the top stem bolt is clamping you’re fine. And so long as you’ve got enough space between the underside of your top cap and the compression bolt to ensure the top cap doesn’t bottom out when providing the preload, you could use the flush fitting Colnago cap.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

User avatar
TonyM
Posts: 2482
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Thanks for the feedback.
This is how I understood it from this thread.

No idea why the LBS did that as I bought the bike a few years ago...

Now having the 5mm spacer on top of the stem doesn’t really provide any improvements, right?


User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

No, the 5mm spacer isn’t necessary or doing anything at all in that scenario. Only reason you’d have a spacer on that is if you think it looks better. One thing... I can’t see how far below the top of the stem the steertube and the compression plug are. Can you remove the top cap, take a pic, and measure the distance from the top of the stem to the top of the plug. A couple of mm’s is fine, but 5mm of recess would be a lot. And let’s have a look at the underside of the top cap to see it has any protrusions that meant the only way to have enough space for preload was with the spacer.
I was in Canada on Wednesday and meant to send you something but completely forgot. I will soon. :).
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

By the way, that stem (the Superlegerra) only has a stack height of around 36mm, right? And the top bolt sits very close to the edge. I am surprised they cut the steertube as short as they did. I would have thought if anything it might have been cut when a more standard 40mm stack height stem was being used. Do you still have the short headset cover that came with the bike (it’s supplied with two... the tall one which you show, and then a shorter one). If you wanted to use a stem with a taller stack height I think you’d be forced to used the short headset cover as the steertube likely wouldn’t be covering the top bolt clamp area in that case.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

User avatar
TonyM
Posts: 2482
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

No problem with the mail!

Well I must have drunk too much last time I checked my stem 🤪 as I rechecked just now and the steerer is almost flush with the stem. It is just 1 mm below the top of the stem.

What would be the optimum height if I use the 5mm spacer on top? Just flush with the stem or 2 mm over the stem for example?


Image

AJS914
Posts: 2048
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

Don't use a spacer on top. Just like slammed, flush looks best anyway.

User avatar
Calnago
Posts: 6228
Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

That is fine. With the compression plug lip it will extend just above the stem, providing a lip for the spacer and enough space for the preload. So for that setup with that stem, you’ve got a petty optimal cut right there. But where is the compression plug?
If you tried to use even the very flat Colnago cap there without a spacer you likely wouldn’t have enough clearance to apply some preload before the underside of the top cap (about a 1mm recess) bottomed out on the edge of the steertube. But you should definitely have the compression cap in there. It’s an aluminum sleeve probably about 10cm long.
And I would absolutely use the 5mm spacer approach with that stem. It is a light stem and that top bolt sits very close to the top edge. Keep it supported. With the compression cap installed it should extend just a bit proud of flush providing a nice lip for the spacer.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

User avatar
Kayrehn
Posts: 1049
Joined: Thu Mar 24, 2011 6:06 pm

by Kayrehn

Like this... 5mm spacer around the plug top, then top cap over it. Image

Sent from my SM-G930F using Tapatalk


User avatar
TonyM
Posts: 2482
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Calnago wrote:That is fine. With the compression plug lip it will extend just above the stem, providing a lip for the spacer and enough space for the preload. So for that setup with that stem, you’ve got a petty optimal cut right there. But where is the compression plug?
If you tried to use even the very flat Colnago cap there without a spacer you likely wouldn’t have enough clearance to apply some preload before the underside of the top cap (about a 1mm recess) bottomed out on the edge of the steertube. But you should definitely have the compression cap in there. It’s an aluminum sleeve probably about 10cm long.
And I would absolutely use the 5mm spacer approach with that stem. It is a light stem and that top bolt sits very close to the top edge. Keep it supported. With the compression cap installed it should extend just a bit proud of flush providing a nice lip for the spacer.
Ok. Good to know it is all good. Thanks.


User avatar
TonyM
Posts: 2482
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Kayrehn wrote:Like this... 5mm spacer around the plug top, then top cap over it. Image

Sent from my SM-G930F using Tapatalk
I suppose this is the maximum height you can go with a 5mm spacer on top, right?

(And I may have the minimum height with my 5mm spacer on top)

Edit: I see now that the compression plug is inside. All good. Thanks.
Last edited by TonyM on Sat Jun 02, 2018 5:12 am, edited 2 times in total.

by Weenie


Post Reply
  • Similar Topics
    Replies
    Views
    Last post